Above-ground tanks for storing liquids such as water and petroleum products have been in widespread use for over a century. In that time various devices have been contrived for enabling a workman associated with tank or tank farm maintenance to quickly judge the level of a liquid substance within a storage tank. One method for judging the level of a liquid in a tank includes a vertical tube mounted to an outside surface of a tank, with a weight suspended within the tube by a cable that is connected at its other end to a float contained within the tank through one or more pulleys. Prior art setups for this have been seen to be relatively complicated, as shown in U.S. Pat. Nos. 1,741,792 and 1,879,805. Such systems, with all their attendant components, make for an expensive way to do what should be a simple task.
Some workers, such as the inventors of U.S. Pat. D 334,718 have attempted to simplify external tank gauges. However, the design provided by these workers is not without inherent problems, as explained further in other parts of this specification. Thus, the present invention provides an inexpensive and reliable means for judging the liquid level in a tank by glancing at an external, mechanically-operated sight gauge.